Processing aid

ABSTRACT

The invention deals with a processing aid for polymeric compositions. The processing aid is a terpolymer comprising 10-49% by weight of a vinyl aromatic monomer like styrene, 5-35% by weight of an acrylic nitrile, like acrylonitrile and 21-60% by weight of an alkylacrylate or alkylmethacrylate with a viscosity number of more than four as measured in dimethylformamide at 30+ C. at a concentration of 100 mg terpolymer per 100 ml dimethylformamide.

FIELD OF THE INVENTION

The invention relates to a terpolymer derived from a vinylaromticmonomer, an acrylic nitrile and an alkylacrylate or alkylmethacrylate.

The invention further relates to thermoplastic resin compositionscomprising the terpolymer according to the invention as a processingaid.

The invention also relates to objects made out of the thermoplasticresin composition according to the invention.

BACKGROUND OF THE INVENTION

Terpolymers derived from a vinyl aromatic monomer, an acrylic nitrileand an alkylacrylate or alkylmethacrylate are known processing aids forvinylhalide (co)polymers. U.S. Pat. No. 2,646,417 describes processingaids in the form of styrene interpolymers made from monomeric mixturescontaining as the two essential monomers from 50 to 90% by weight ofstyrene and from 10-50% by weight of an acrylic nitrile, in which othermonolefinic monomers like ethylacrylate, vinyl acetate, vinyl benzoate,methyl methacrylate may be present but only in minor amounts of lessthan 20% by weight. Said known processing aids are used in a quantity of1 to 10% by weight to lower the processing temperature ofnon-plasticized vinyl halide resins. The known processing aids should be"high in molecular weight".

The one example dealing with terpolymers describes a terpolymer of 65%by weight of styrene, 25% acrylonitrile and 10% by weight ofethylacrylate.

U.S. Pat. No. 3,975,315, corresponding with FR-A-2,062,817 describes"copolymers of a styrene containing about 10 to 40% of a boundacrylonitrile or 25 to 75% of an alkyl substituted acrylate or both".Said copolymers should have a "dilute solution viscosity greater thanabout 1.5". By incorporating 5 to 20 weight parts, per 100 weight partsof a vinylchloride polymer, of said copolymer the vinylchloride whenexpanded has upon extrusion sufficient hot strength. According to thisprior art it is preferred to use copolymers with greater than 50%, evenmore preferred with 60 to 90 weight percent of styrene and 10 to 40weight percent of acrylonitrile, more preferably 15 to 35%. The styrenecopolymer may also contain an alkyl methacrylate or ethacrylate inaddition to, or in place of, the nitrile in amounts from 5 to 75%,preferably 40 to 60%. The "dilute solution viscosity" of the copolymeris preferably greater than 2.5. It seems to have been determined in a 1%monochlorobenzene solution at a non-disclosed temperature.

FR-A-1.600.621 mentions in very general terms the possibility to usehigh molecular weight methyl-methacrylate-styrene-acrylonitrileterpolymers as an agent to make polymers more suitable for expansion.

SUMMARY OF THE INVENTION

The present invention deals with novel terpolymers which may be used asa processing aid for thermoplastic resin compositions. The terpolymersaccording to the invention have been derived from a vinylaromaticmonomer, an acrylic nitrile and an alkylacrylate or alkylmethacrylate.

The terpolymers according to the invention have the followingadvantageous properties:

They can be incorporated in thermoplastic resin compositions such as forexample compositions comprising a vinylhalide polymer or copolymer. Whenincorporated in such thermoplastic compositions they decrease the geltime thereof, they improve the thermal stability thereof, they aredispersable, they improve the visco-elasticity thereof and they increasethe hot elongation thereof.

A further advantage of the terpolymers according to the invention isthat they can be made easily with a very low residual styrene monomercontent (of less than 500 ppm after drying). This is important forapplications where the thermoplastic resin composition comprising theterpolymer according to the invention comes into contact with food.

The terpolymer according to the invention further offers the advantagethat by changing the ratio of the monomers in it one may adopt therefractive index to match the refractive index of the thermoplasticpolymer in which it is incorporated.

In view of the above indicated properties the terpolymers according tothe invention can be used as a processing aid for vinylhalide(co)polymers to make them better suitable for calendering, extrusion,blow moulding, injection moulding, expansion into foam and for makingbi-oriented materials such as described for example in FR-A-8123149.

DETAILED DESCRIPTION

The terpolymers according to the invention are characterized in that theterpolymer comprises

10-49% by weight of the vinylaromatic monomer,

5-35% by weight of the acrylic nitrile and

21-60% by weight of the alkylacrylate or alkylmethacrylate

and has a reduced viscosity of more than four as measured indimethylformamide at 30° C. at a concentration of 100 mg terpolymer per100 ml dimethylformamide.

It is preferred to have a terpolymer which comprises

26-49% by weight of the vinylaromatic monomer,

5-14% by weight of the acrylic nitrile and

37-60% by weight of the alkylacrylate or alkylmethacrylate

and has a reduced viscosity of five or more as measured indimethylformamide at 30° C., at a concentration of 100 mg terpolymer per100 ml dimethylformamide.

The present invention also deals with thermoplastic resin compositionscomprising at least one thermoplastic resin and a polymeric processingaid characterized in that the composition comprises as a processing aida terpolymer comprising

10-49% by weight of a vinylaromatic monomer,

5-35% by weight of an acrylic nitrile and

21-60% by weight of an alkylacrylate or alkylmethacrylate,

with a reduced viscosity of more than four as measured indimethylformamide at 30° C., at a concentration of 100 mg terpolymer per100 ml dimethylformamide.

The thermoplastic resin composition comprises preferably as a processingaid a terpolymer comprising

26-49% by weight of the vinylaromatic monomer,

5-14% by weight of the acrylic nitrile and

37-60% by weight of the alkylacrylate

or alkylmethacrylate, with a reduced viscosity of five or more measuredin dimethylformamide at 30° C., at a concentration of 100 mg terpolymerper 100 ml dimethylformamide.

The thermoplastic resin composition can comprise a vinylhalide(co)polymer and a processing aid in a quantity of 0.1-20 parts by weightper 100 parts by weight of the vinylhalide (co)polymer.

The invention further includes objects formed out of the thermoplasticcomposition according to the invention.

The terpolymer according to the invention comprises 10-49% by weight ofthe vinylaromatic monomer, 5-35% by weight of the acrylic nitrile and21-60% by weight of the alkylacrylate or alkylmethacrylate. It has aviscosity number of more than four as measured in dimethylformamide at30° C., at a concentration of 100 mg terpolymer per 100 mldimethylformamide.

As vinylaromatic monomer may be used styrene, alpha methylstyrene,halogenated styrene, vinyltoluene, alkoxystyrene and other styrenederivates that are copolymerisable with an acrylic nitrile and analkyl(meth)acrylate.

Suitable acrylic nitrile monomers are for example methacrylonitrile,ethacrylonitrile, chloroacrylonitrile, acrylonitrile and the like.

Suitable alkylacrylates and alkylmethacrylates are for example methyl-and ethylacrylate and the corresponding methacrylates.

The viscosity number of the terpolymer according to the invention iscritical: it should be above four, by preference five or more measuredas indicated above. When the viscosity number is four or lower one doesnot obtain the desired improvement in visco-elasticity and hotelongation.

This viscosity number has been determined as further outlined in theexamples.

The relative amounts of the monomers in the terpolymer as indicatedabove are critical also for achieving the desired results.

The terpolymers according to the invention can be incorporated inthermoplastic resin compositions in order to improve the propertiesthereof. Suitable thermoplastic polymers are polystyrenes andpolyphenylene ethers. Particularly suitable seem at present the polymersand copolymers derived from vinylhalide monomers.

EXAMPLE I: Preparation of the Terpolymer

Several terpolymers with different viscosity numbers have been preparedas follows.

A 16 liter batch reactor was filled with 8880 grams of deionised water,2 grams sodium phosphate, 2 grams potassium persulfate and 56 gramssodium dodecylsulfate. The contents were agitated (with a stirrerrotating at 200 rounds per minute). The contents were degassed byevacuation; subsequently the reactor was filled with nitrogen. Thereactor was heated to 65° C. Upon reaching a temperature of 50° C. thefollowing monomers were added: 560 grams acrylonitrile, 1920 gramsstyrene and 1520 grams methylmethacrylate. The monomers were reacted for4 to 7 hours at 65° C. Total conversion after 7 hours was about 99%.

The product as obtained above was destabilised by pouring it understirring in a 10% by weight calcium chloride solution with a temperatureof 92° C. The obtained flocculated product was centrifugated and driedin a fluid bed at 80° C. for one hour. The so obtained dry powder wasseeved to a particle size below 1 mm. The chemical composition of theobtained terpolymer after 7 hours was as follows: 48% by weight styrene,14% by weight acrylonitrile and 38.0% by weight methylmethacrylate, witha refractive index N of 1.545. The so obtained powders were utilised inthe examples.

EXAMPLE II: Determination of the Viscosity Number

50 milligrams of the terpolymer powder were dissolved in 50 ml filtereddimethylformamide. About 15-20 ml of the obtained solution were broughtinto an Ubbelhode viscosimeter (placed in a thermostatic bath at 30°C.). The used viscosimeter possessed an out flow constant (c) of about0.004672. The inner diameter of the capillary tube was 0.53 millimeter.The time lapsed for passing of the solution over a well defined, fixeddistance in the viscosimeter was measured five times, with an accuracyof about 0.1 seconds. A similar measurement was performed for thesolvent separately without any terpolymer dissolved therein. Theviscosity number was calculated as follows: ##EQU1## wherein t is thetime for the solution, t₀ the time for the pure solvent and P the numberof grams terpolymer per 100 ml solvent.

It has been tried to determine the viscosity of a terpolymer accordingto the invention with a viscosity number of about 5, determined asindicated above, in a 1% monochlorobenzene solution as indicated in col.6, line 40 of U.S. Pat. No. 3,975,315. The terpolymer according to theinvention did not dissolve at 30° C. in monochlorobenzene. By making amonochlorobenzene solution of 0.1% by weight of one reaches a value forthe viscosity number of 7.6 which is far above the values mentioned inU.S. Pat. No. 3,975,315.

Total of 5 terpolymers have been prepared with viscosity numbers of 2,5, 6, 7, 8 dl/g respectively.

The residual content of monomers in the terpolymer with a viscositynumber of 7 dl/g was as follows: styrene about 370 ppm;methylmethacrylate about 300 ppm and acrylonitrile below 10 ppm.

EXAMPLE III: Preparation of Thermoplastic Composition

Said terpolymers were incorporated in a rigid polyvinyl chloridecomposition with the following ingredients:

    ______________________________________                                                            Parts by weight                                           ______________________________________                                        PVC-resin with K-value 57-58                                                                        100                                                     epoxidised soja beanoil                                                                             2                                                       Irgastab 17 (stabiliser)                                                                            1.5                                                     tris-(nonylphenyl)phosphite (TNPP)                                                                  0.5                                                     Calciumstearate       0.3                                                     Loxiol G15            1.5                                                     Blend of three waxes  0.7                                                     terpolymer according to the                                                   invention, in quantities as                                                   indicated below for the described                                             tests.                                                                        ______________________________________                                    

2 Parts by weight of the terpolymer prepared as indicated hereabove witha viscosity number of 7 dl/g were incorporated in the above mentionedPVC composition. All components were blended in a high speed mixer at120° C.

EXAMPLE IV: Determination of Gel Time, Thermal Stability

The so obtained composition (60 cm³) was tested in a Brabenderplastograph at 170° C., at 30 rpm to determine the gel time=fusion time.This is the time period from the start of blending till a maximum in thetorque has been reached. For comparative purposes the gel time has alsobeen determined for the same PVC composition without terpolymer. Theresults were as follows:

    ______________________________________                                                         Gel time (minutes)                                           ______________________________________                                        PVC without terpolymer                                                                           8.00                                                       PVC with 2 parts terpolymer                                                                      4.00                                                       ______________________________________                                    

As can be seen the gel time is greatly reduced by incorporating theterpolymer according to the invention.

A similar PVC composition as tested above with 8 parts by weight of theterpolymer with a viscosity number of 7 dl/g was tested for its thermalstability. To this end the composition was processed into a foamedsheet. The test specimen was taken after a certain time from a two rollmill at 200° C.

After 10 minutes the composition hardly showed any yellowing; after 15minutes some light yellowing occurred. This is similar as for PVCcompositions without terpolymer.

EXAMPLE V: Determination of the Elasticity of Molten PVC

A series of PVC compositions was prepared with a composition asindicated above, to which 2 parts by weight of a terpolymer with anindicated viscosity number, prepared as indicated above, was added. As acontrol a composition without terpolymer has been tested.

                  TABLE A                                                         ______________________________________                                        PVC composition                                                               with 2 parts                                                                  terpolymer of indicated                                                       viscosity (dl/g) Hot elongation (%)                                           ______________________________________                                        CONTROL          320                                                          2                360                                                          5                580                                                          6                640                                                          7                680                                                          8                720                                                          ______________________________________                                    

The results show that there is a critical value for the viscosity numberof about 4, possibly 5.

EXAMPLE VI: Determination of Visco-elasticity

A series of similar PVC compositions as indicated above to which hadbeen added 0.5 parts by weight of a terpolymer with various viscositynumbers, prepared as indicated above, were tested for blow mouldingtwenty (1 liter) bottles of each composition. Average extrusiontemperature was about 170° C. The parison was extruded through a diewith an outer diameter of 31 mm and an inner diameter of 29.7 mm. Theextruder operated at 25 rounds per minute. The relative increase inweight of the bottles (%) as compared to bottles made of a control PVCcomposition without terpolymer was determined. This is a good measurefor the visco elasticity i.e. the higher the weight increase the greaterthe increase in viscoelasticity of the molten PVC. A greaterviscoelasticity is of importance to get a better control of the wallthickness of the parison. The obtained results are summarized in tableB.

                  TABLE B                                                         ______________________________________                                        PVC composition                                                               with 0.5 parts                                                                terpolymer of                                                                 viscosity number                                                                              Increase in weight                                            in dl/g         of the bottle (%)                                             ______________________________________                                        2               2                                                             5               10                                                            6               13                                                            7               14.5                                                          8               16                                                            ______________________________________                                    

Here again it can be seen that there is a critical limit for theviscosity number of about 5 dl/g.

We claim:
 1. Terpolymer derived from a vinylaromatic monomer, an acrylicnitrile and an alkylacrylate or alkylmethacrylate, characterized in thatthe terpolymer comprises10-49% by weight of the vinylaromatic monomer,5-35% by weight of the acrylic nitrile and 21-60% by weight of thealkylacrylate or alkylmethacrylateand has a viscosity number of morethan four dl/g as measured in dimethylformamide at 30° C. at aconcentration of 100 mg terpolymer per 100 ml dimethylformamide. 2.Terpolymer according to claim 1, characterized in that the terpolymercomprises26-49% by weight of vinylaromatic monomer, 5-14% by weight ofthe acrylic nitrile and 37-60% by weight of the alkylacrylate oralkylmethacrylateand has a viscosity number of five dl/g or more asmeasured in dimethylformamide at 30° C. at a concentration of 100 mgterpolymer per 100 ml dimethylformamide.